1. Technical Field
The present disclosure relates to a method and an apparatus for generating a PWM signal. More specifically, the present disclosure relates to a method and an apparatus for generating a random PWM voltage reference signal for driving an inverter, which can more simply generate random position PWM (RPPWM) in which a position of an active vector is changed to achieve the same effect as when a switching frequency is changed.
2. Description of the Related Art
In the case where an inverter is driven by a PWM signal having a fixed frequency, voltage and current are concentrated on a multiplied frequency of the switching frequency. As a result, there is a problem in that noise of a particular frequency is created.
In order to solve the problem, a random PWM scheme that varies the switching frequency has been proposed. The schemes for implementing such random PWM may include random frequency PWM (RFPWM) that varies the frequency of a triangle wave itself, random position PWM (RPPWM) that varies the position of an active vector, random switching PWM (RSPWM) that generates a random number of pulses, and the like.
Among these, in the RFPWM scheme, the frequency of a triangle wave itself is randomly varied.
When the current of a general-purpose inverter is measured, a triangle wave is sampled at its peak or zero. Accordingly, whenever the frequency of a triangle wave is changed, sampling timing is changed at every period.
Since a fixed switching frequency has a constant period of a triangle wave in operation processes necessary for reference frame conversion, it is may not necessary to calculate calculation periods at every PWM period. However, when the frequency of a triangle itself is changed such as in RFWPM scheme, calculation periods are changed at every period and thus are calculated at every period of a PWM signal. As a result, there are many considerations in programming, and calculation time also increases.
In view of the above, according to an exemplary embodiment of the present disclosure, RPPWM can be implemented more simply, such that it can be widely applied to general inverters and reduce electromagnetic noise of inverters effectively.